Expansion of the wireless communication arena is being driven by an increasing demand for wireless devices along with improvements in wireless communications platforms and systems. Users may exchange information through pagers, cellular telephones other wireless communications and computer based products. Wireless communication provides users the benefit of exchanging personal and business information employing wireless networks such as a wireless local area network (WLAN). A WLAN provides flexibility and mobility for users by enabling access to a spectrum of communication and computer networks, including the Internet, without being restricted to a wired network.
Several standards have been established to provide uniformity and support growth in the development of wireless networks. One such standard that has been promulgated by the Institute of Electrical and Electronic Engineers (IEEE) is IEEE 802.11, which is incorporated herein by reference. IEEE 802.11 is an overarching standard that encompasses a family of specifications pertaining to wireless communication. Generally, IEEE 802.11 specifies an over-the-air interface between a wireless client and a base station or between two wireless clients.
Within the IEEE 802.11 family are several specifications covering topics such as different transmission rates, encoding schemes and frequency bands for transmitting data wirelessly. For example, IEEE 802.11a is an extension of IEEE 802.11 that specifically addresses WALES having a data rate up to 54 Mbps and employing a carrier frequency of five GHz. Additionally, IEEE 802.11a specifies an orthogonal frequency division multiplexing (OFDM) encoding scheme.
Multiple-input multiple output (MIMO) communication systems provide improvements in capacity and reliability over single-input single-output (SISO) communication systems and may be employed to advantage in wireless networks and communication systems. The MIMO communication systems commonly employ a block structure wherein a MIMO transmitter, which is actually a collection of single-dimension transmitters, sends a vector of symbol information. This symbol vector may represent one or more coded or uncoded SISO data symbols. A MIMO receiver, which is a collection of single-dimension receivers, receives one or more copies of this transmitted symbol vector. The performance of the entire communication system hinges on the ability of the receiver to find reliable estimates of the symbol vector that was transmitted.
A 2×2 MIMO communication system may transmit two independent and concurrent signals employing two single-dimension transmitters having separate transmit antennas and two single-dimension receivers having separate receive antennas. When currently employing IEEE 802.11a/g, a SIGNAL field is transmitted in order to convey parameters (such as rate, length, etc.) associated with a data field. The rate portion of the SIGNAL field conveys information about the type of transmit modulation employed, and a coding rate used in the remainder of a packet. The length portion of the SIGNAL field indicates a number of octets in a physical layer supporting the transmission. For such MIMO communication systems, there may also be multiple or additional MIMO modes that may be selected. The existing SIGNAL field generally cannot accommodate all of these options, especially for a legacy MIMO communication system employing IEEE 802.11a/g wherein backwards compatibility is to be maintained.
Accordingly, what is needed in the art is a way to provide additional transmission mode information that fits within a current transmission framework.